A tropical wave in the western Caribbean approaching Mexico's Yucatan Peninsula is generating disorganized thunderstorms. Wind shear is a moderate 10 - 15 knots over the region, and water vapor satellite images show that there is some dry air to the west that will interfere with any development that might occur. None of the reliable computer models develop this wave, and NHC is giving it a 10% chance of developing into a tropical depression.

Figure 1. Morning satellite image of the disturbed region of weather of the coast of Africa, south of the Cape Verdes Islands.

The GFS, NOGAPS, and ECMWF models continue to predict that a tropical storm will form between Africa and the Lesser Antilles Islands sometime in the period 3 - 6 days from now. There is an area of disturbed weather south of the Cape Verdes Islands, but there is no obvious organization to the cloud pattern. Wind shear is a hefty 20 - 30 knots in the region, and the disturbance is a 1 - 2 day journey away from reaching a lower shear area where development can occur. Preliminary indications are that if a storm did develop in this region, it would track west-northwest and pass well to the northeast of the Lesser Antilles Islands 7 - 8 days from now. However, 7-day forecasts of a storm that hasn't even formed yet are not to be trusted.

Figure 2. The cold front that brought an end to the Great Russian Heat Wave of 2010 lies east of Moscow in the NASA MODIS photo taken at 8:35 UTC August 19, 2010. Smoke from wildfires is visible over a wide swath of Russia east of the front. Image credit: NASA.

The Great Russian Heat Wave of 2010 endsA powerful cold front swept through Russia yesterday and today, finally bringing an end to the Great Russian Heat Wave of 2010. Temperatures at Moscow's Domodedovo airport hit 25°C (77°F) today, which is still 4°C (7°F) above average, but the high temperature since late June. Moscow has seen 62 consecutive days with a high temperature above average, but the latest forecast for Moscow predicts that remarkable string will come to an end Friday, when the high will reach just 17°C (62°F).

Massive 926 mb extratropical storm generating huge waves off AntarcticaOne of the most intense extratropical storms in recent years is churning up the waters near the coast of Antarctica in the South Indian Ocean. The powerful storm peaked in intensity yesterday afternoon with a central pressure of 926 mb--the type of pressure typically found in a Category 4 hurricane. Storms this intense form on average once per year, or perhaps less often, according to an email I received from Jeff Callaghan of the Australia Bureau of Meteorology. Since extratropical storms do not form eyewalls, the winds at the surface from this monster storm probably reached "only" 100 - 120 mph (equivalent to a Category 2 or 3 hurricane.) The storm is forecast to generate huge waves with a significant wave height of 13 meters (44 feet) today, according to the NOAA Wavewatch III model (Figure 3.) I have flown into an extratropical storm this intense--in 1989, I participated in a field project based in Maine that intercepted a remarkable extratropical storm that "bombed" into a 928 mb low south of the Canadian Maritime provinces. You can read my story of that somewhat harrowing flight here.

Figure 3. Satellite image taken at 8:10 UTC August 19, 2010, showing the intense extratropical cyclone that has weakened to 940 mb in the South Indian Ocean near the coast of Antarctica. Image credit: NASA.

Figure 4. Surface pressure analysis from 18 UTC August 18, 2010, showing a 926 mb low in the South Indian Ocean, just north of Antarctica. Image credit: Jeff Callaghan, Australia Bureau of Meteorology.

Figure 5. Predicted wave height from the NOAA Wavewatch III model for 2pm EDT (18 UTC) today, August 19, 2010. Peak wave heights of 13 meters (44 feet) are projected over ocean areas between Antarctica and Australia. Long-period waves (19 seconds between crests) up to 7 meters (22 feet) high are predicted to affect the southwest coast of Australia by Sunday. The waves are predicted to propagate eastwards to New Zealand 8 - 9 days from now, and be a respectable 4 - 5 meters high then.

USED A BLEND OF THE 00Z ECMWF AND ITS ACCOMPANYING 50 MEMBERENSEMBLE MEAN TO UPDATE THE FRONTS AND PRESSURES FOR DAYS 3THROUGH 7. ALL IN ALL...THE VARIOUS MODELS AND ENSEMBLE MEANS AREIN GOOD AGREEMENT THIS PERIOD...SHOWING A SUBSTANTIAL FULLLATITUDE COLD FRONT KNIFING ACROSS THE PLAINS...AND ACLOSED...STACKED...CYCLONIC CIRCULATION HOLDING ITS GROUND...ORSHOULD SAY OCEAN SURFACE...OVER THE WESTERN ATLANTIC. THEMERIDIONAL FLOW HAS A DISTINCT POSITIVE TILT ACROSS THE UNITEDSTATES...WHICH ALLOWS THE ATLANTIC TROUGH TO JUST SLOWLY SHEARAPART IN PLACE...OR DRIFTING SOUTHWARD WITH TIME. THE ECENS MEANIS STILL PERFORMING STRONGLY ENOUGH AT THE DAY 6 TO 7 TIME RANGETO RELY ON ITS VERSION OF THE ATMOSPHERE OVER THE OTHER GUIDANCE.

FINAL...

NO SURPRISES WITH THE 12Z GUIDANCE...WITH THE PATTERN ILLUSTRATEDBY THE UPDATED MANUAL PROGS STILL SUPPORTED BY BOTH THEDETERMINISTIC AND ENSEMBLE MEANS FROM THE VARIOUS CENTERS. COORDINATED THE LOW DRIFTING WESTWARD ACROSS THE NORTHERN GULF OFMEXICO WITH TPC DURING THE MIDDAY CALL...AS SUCH CIRCULATIONSBREAKING OFF FRONTAL ZONES DO BECOME TROPICAL FROM TIME TO TIME. HOW FAR OFF THE MID ATLANTIC COAST THE SYNOPTIC LOW ENDS UPFORMING IS STILL UNCERTAIN...BUT HAVE THE POWER OF THE HIGHLYRESOLVED ECENS MEAN MEMBERS TO BACK UP THE FINAL MANUAL DEPICTION.

Quoting xcool:Homegrown Development Possible In The Northern Gulf of Mexico or Off Of The US Southeast Coast This Weekend Into Next Week:We may be watching things much closer to home over the next seven to ten days as there may be things that try to develop underneath the radar.

The first item to watch is a low pressure system that is forecast to develop just off of the coast of northeast Florida late this weekend. This low pressure system will initially be non-tropical in nature, however, it may acquire tropical characteristics as it tracks southwest and then westward across the northern Gulf of Mexico throughout much of next week. It is unknown right now how long it may remain over the Gulf of Mexico waters, however, the potential is there for slow development into a tropical cyclone and it will be watched for as we head into this weekend.

Homegrown Development Possible In The Northern Gulf of Mexico or Off Of The US Southeast Coast This Weekend Into Next Week:We may be watching things much closer to home over the next seven to ten days as there may be things that try to develop underneath the radar.

The first item to watch is a low pressure system that is forecast to develop just off of the coast of northeast Florida late this weekend. This low pressure system will initially be non-tropical in nature, however, it may acquire tropical characteristics as it tracks southwest and then westward across the northern Gulf of Mexico throughout much of next week. It is unknown right now how long it may remain over the Gulf of Mexico waters, however, the potential is there for slow development into a tropical cyclone and it will be watched for as we head into this weekend.

August 21, 2006: Tropical Storm Debby passed south of the Cape Verde Islands as a tropical depression. A tropical storm warning was issued for the Cape Verde Islands, but was discontinued when Debby turned further westward and away from the islands.

the main concern in the short term is the continued potential for heavy rain over south central and east central Louisiana as well as southwest Mississippi in association with primarily what is now the middle level remnants of what was once upon a time tropical depression 5. Models maintain the middle level remnants of this system over east/south central Louisiana and southwest Mississippi today before weakening and shearing out the feature tonight and Friday. We plan to maintain the Flash Flood Watch today for southwest Mississippi and those areas of southeast Louisiana along and to the west of a line from Washington Parish to St. John The Baptist Parish. This generally corresponds to the areas that have seen the most rain over the past few days.

Showers and thunderstorms will still be prevalent on Friday as considerable deep moisture hangs around. Upper level ridging will amplify over the plains over the weekend...but the greatest influence of this ridging will remain west of the region. Some drier air will attempt to work into the forecast area on Saturday...so Saturday will likely be a lower pop day. As the ridging builds over the plains...an upper trough will traverse the New England and middle Atlantic regions late in the weekend and early next week. This will push a weak cold front into the southeast U.S. And Gulf Coast region. This boundary should serve as a focus for convection next week. In addition...a number of the medium range models forecast a middle level feature...with an eventual surface reflection forming in the the vicinity of the front or north Gulf...in the Atlantic off the southeast coast moving west into the north Gulf during the early and middle week period of next week. This could lead to another rather wet period. 11

Okay, I'll explain it. First of all.. none of them had strong model support, persistence and actually gained convection off the coast (exception is Colin, but that also had model support for development) and the reason they all go 'poof' is simple, the change from land to water usually causes the wave to dissipate. There are about 50 or so waves that come off the African coast each year, and 4-5 develop that are pure Cape Verde originated.

Too add to that, this wave has very good amounts of rotation. 850 mb vort is pretty impressive, probably our most vigorous wave all year.

Quoting xcool:Long term (saturday night through next thursday)...models continue to indicate an amplifying trough along the eastern Seaboard which will push a cold front down into the local region early next week. The front should stall over or just north of our County Warning Area. The GFS develops a wave on or near the boundary in the northeast Gulf Monday and drifts it westward over la on Tuesday. This looks very similar to what we just saw with the remnant low of dew point 5. Time height cross sections show deep layer moisture in place at least through Monday and plenty of upper level energy. This along with daytime heating and sea-breeze interaction with the stalled boundary will result in above seasonal chances for showers and thunderstorms though Monday. If the GFS solution verifies and the surface low pulls further west on Tuesday we may see convection trending back to more seasonal levels (40%) Tuesday through the remainder of the extended period. Maximum temperatures will generally be in the lower 90s and min temperatures will be in the lower to middle 70s.

Quoting CosmicEvents:No, it was said directly by at least one and inferred by many. By at least one "expert"(MH09). I'll go back and look through thousands of posts if anyone cares to wager substantially on it.

Expert? Um, no. If you find the post I'll be glad to read it, but I sure don't remember it.

I'll grant you that but I think we have seen about a hundred of them this year that just go away. No rotation at all and just vaporize out there in the Atlantic. I wish someone would try to explain why this keeps happening. I know some of them have be destroyed by shear but the lack of development is way beyond my expertise.

Okay, I'll explain it. First of all.. none of them had strong model support, persistence and actually gained convection off the coast (exception is Colin, but that also had model support for development) and the reason they all go 'poof' is simple, the change from land to water usually causes the wave to dissipate. There are about 50 or so waves that come off the African coast each year, and 4-5 develop that are pure Cape Verde originated.